The present invention relates to a method and an apparatus for adjustment in mold thickness of a complex mold clamping system in injection molding machines, and more particularly to a method and an apparatus for adjustment in mold thickness to allow simplification of a half-nut screw engaging position adjusting feature used in die thickness adjustment.
A toggle type mold clamping system and a straight hydraulic mold clamping system have been well known as major mold clamping systems. By contrast, a complex mold clamping system is minor but attractive in possibility of scaling down in whole of the mold clamping system as compared to the major toggle type or straight hydraulic mold clamping systems. This complex mold clamping system is provided with a specific mold thickness adjusting system which will hereinafter be described with reference to FIGS. 1 and 3.
The complex mold clamping system essentially comprises the following elements. A pair of fixed and movable dies 10 and 14 are provided on a fixed platen 12 and a movable platen 16 respectively. Mold opening and closing cylinders 18 are provided at the edges of the fixed platen 12. The mold opening and closing cylinders 18 are mechanically connected via cylinder rods 18a to the movable platen 16. The movable platen 16 is unitary formed with a holder 26 which is slidably placed over a base 28. The fixed platen 12 and the mold opening and closing cylinders 18 are fixed on the base 28. A mold clamping cylinder 22 is movably placed on the holder 26. The mold clamping cylinder 22 is connected to the fixed platen 12 through tie bars 20 which are provided with screw portions 20a.
The mold clamping cylinder 22 is also coupled to the movable platen 16 through a cylinder ram 24. A screw engaging position adjuster 40 is further provided on the movable platen 22. Half nuts 30 are provided on the movable platen 16 so that the movable platen 16 is selectively engaged through the half nuts 30 to the tie bar screw portions 20a. After the fixed platen 12 and the movable platen 16 are closed to each other by the mold opening and closing cylinders 18 but before the fixed platen 12 and the movable platen 16 are clamped by the mold clamping cylinder 22, the half nuts 30 are engaged with the tie bar screw portions 20a through the screw engaging position adjuster 40 for adjustment in thickness of the fixed and movable dies 10 and 14. A mold thickens adjusting system comprises a control driver 50, the half nuts 30 operable under the control of the control driver 50 and the screw engaging position adjuster 40 connected to the control driver 50. FIGS. 1 and 2 are illustrative of the complex mold clamping system in the opened state and in the closed state respectively.
FIG. 4 is illustrative of the screw engaging position adjusting system of the complex mold clamping system. As illustrated in FIG. 4, the control driver 50 comprising a controller unit and a driver unit. The controller unit comprises a detector 52, an arithmetic unit 54 and a controller 56. The driver unit comprises an operational cylinder 32 for engagement of the half nuts 30 and a rotary driving hydraulic motor 42 of a sprocket 44 of the screw engaging position adjuster 40. The detector 52 is so designed as to detect a moving distance L between the mold thickness adjustment origin position P of the movable platen 16 and the clamped position P' thereof through an operational pressure "PC" of the mold opening and closing cylinders 18, where the following formula is given. EQU L/p=N+.DELTA.L
where p is the pitch of the half nuts 30 and the tie bar screw portions 20a, N is the integer and .DELTA. L is the theoretical deviation of the screw engagement position when the engagement screw pitch is less than "p". The arithmetic unit 54 is so designed as the convert .DELTA. L into a rotation number "n" for the sprocket 44.
In FIG. 1, the movable die 14 and the fixed die 10 are distanced from each other wherein the half nuts 30 are in the opening state. Then, the movable die 14 and the fixed die 10 come closed to each other by the mold opening and closing cylinders 18 as illustrated in FIG. 2. Subsequently, the sprocket 44 is rotated at a predetermined rotation "n" by the rotary driving hydraulic motor 42 for adjustment of the mold thickness before the half nuts 30 are engaged with the tie bar screw portions 20a under the operations of the operational cylinder 32 as illustrated in FIG. 3B.
The sprocket 44 has a contract surface 44b which is to be in contact with a contact member 24b placed through a spring 44c and around a base of a projecting screw axis 24a. After the half nut 30 was engaged with the tie bar screw portions 20a, a hydraulic port 22a of the clamping cylinders 22 is opened and pressure is applied through another hydraulic port 22b so that the fixed and movable dies 12 and 16 are closed. Thereafter, the half nuts 30 are opened by an operational cylinder 32 as illustrated in FIG. 3C, before the fixed and movable dies 12 and 16 are clamped through the mold opening and closing cylinders 18 as illustrated in FIG. 2.
According to the above method of adjustment of the molding thickness, a substantially continuous operation is possible in exchanging the dies.
The method of adjustment in the molding thickness of the above complex mold clamping system, however, has the following disadvantages.
As described above, the screw engaging position adjuster 40 comprises the sprocket 44 which is usually engaged via screw to a projection screw axis 24a on the ram 24 so that the sprocket 44 is mechanically driven by a hydraulic motor 42 through a transmission system 44a. The sprocket 44 is thus placed in front of a center portion of the mold clamping cylinder 22 and further the contact surface 44b is made into contact with the contact member 24b placed through the spring 44c and around the base of the projecting screw axis 24a. For those reasons, the screw engaging position adjuster 40 is structurally complicated and the maintenance works are trouble. Further, it is difficult to reduce the scale of the system and there is a limitation in place where the system is placed.
As a returning member, the springs are used, for which reason in the injection and compression molding, if the die opening amount is beyond 5 mm by a presumable high pressure of the injection resin, the above system is not responsible.